This invention relates to compounds useful as lubricants per se or as wax and resin additives providing excellent lubricating or low friction properties. The solid lubricants of this invention can be brittle and hard solids or can have the physical properties of waxes. Waxes are defined as substances which are plastic solids at ambient temperature and, on being subjected to moderately elevated temperatures, become low viscosity liquids. Waxes having low frictonial properties are of special importance as ski waxes. Some of the compounds described in this invention are not having the solid state properties of waxes but are important as additives to waxes and resins and especially to hydrocarbon waxes providing low friction properties.
It is well known that different types of ski waxes are being used to achieve the smoothest gliding and therefore highest speed under different snow and weather conditions. In ski racing, for instance, a difference of one-hundredth of a second can mean winning or losing a race; and therefore, the selection of the right type of ski wax for a given snow and weather condition is most important.
It is also well known that most ski waxes used today are hydrocarbon waxes having different hardness and melting points. Hydrocarbon waxes used as ski waxes are paraffin waxes consisting principally of normal alkanes or synthetic waxes such as low molecular weight polyethylene having wax-like properties.
Hydrocarbon ski waxes with melting points below 50.degree. C. are too soft and not sufficiently abrasion resistant, while hydrocarbon waxes with melting points much above 100.degree. C. would damage ski bases made of extruded or sintered polyethylene, when applied as a hot melt, since polyethylene has a melting point of approximately 120.degree. C.
Depending on the type of snow, snow temperature and snow moisture, as well as air temperature and air humidity, the following type of ski waxes are recommended to achieve the highest speed and best control:
The softest and lowest melting hydrocarbon waxes are recommended for snow temperatures of -3.degree. to -4.degree. C. and above.
Medium hard, higher melting hydrocarbon waxes are recommended for snow temperatures in the range of -3.degree. to -10.degree. C.
The hardest and highest melting hydrocarbon waxes are recommended for snow temperatures of about -10.degree. C. and below. Commercial hydrocarbon based ski waxes were found to have melting points as low as 55.degree. C. and as high as 95.degree. C.
By mixing ski waxes of the above type in different ratios, ski waxes can be tuned to specific conditions present on a racing parcour in order to take other variables besides snow temperature into account.
In addition to snow temperature, the following will influence how much softer or harder the optimum hydrocarbon ski wax has to be:
For softer, less abrasive snow and snow with high humidity content, softer hydrocarbon waxes give better results.
For harder, more abrasive snow and snow with low humidity content, harder and more abrasion resistant hydrocarbon waxes give better results.
If skis are in contact with the snow for seconds or minutes such as in ski-jumping and alpine ski racing, somewhat softer and less abrasion resistant waxes can be used, while for cross country racing lasting hours, harder and more abrasion resistant hydrocarbon waxes are preferred.
While hydrocarbon waxes with melting points between 50.degree. and 100.degree. C. offer the ski racer a lot of flexibility to achieve the highest speed under many different conditions, it has been found that certain perfluorocarbons are superior ski waxes if used under certain snow conditions.
U.S. Pat. No. 4,724,093 describes solid lubricants consisting of solid perfluorocarbons with linear or substantially linear carbon atom chain, containing from 10 to 20 carbon atoms and having surface tensions ranging from 13 to 15 dyne/cm. Perfluorocarbons as described in U.S. Pat. 4,724,093 have melting points which range from 36.degree. C. for C.sub.10 F.sub.22, to 70.degree. C. for C.sub.13 F.sub.28 and 108.degree.-110.degree. C. for C.sub.16 F.sub.34. Fluorocarbon blends used commercially have melting points as high as 108.degree. C.
Because of the low critical surface energy of 13 to 15 dyne/cm, fluorocarbons of the above type have superior water and oil repellent properties. The superior water repellency of these perfluorocarbons make them superior to hydrocarbon waxes on snow having a temperature close to or at the freezing point and on very wet snow. Skis treated with the more hydrophobic (water repellent) perfluorocarbons will glide easier on the water layer generated between the ski base and the snow. The speed retarding suction effect caused by too heavy a layer of water between the ski base and the snow is reduced and speed, therefore, increased. It is also claimed that the oil repellent properties of the perfluorocarbons will reduce the contamination by oily soil, which reduces speed and is of special importance in cross country racing.
While the costly perfluorocarbons have shown their superiority over hydrocarbon waxes on wet snow, and are commercially used in ski racing, they have also been shown to have limitations if compared with the flexibility, safety and low cost that the hydrocarbon waxes offer.
Hydrocarbon waxes are miscible with each other and, therefore, give the ski racer the possibility to prepare the right wax blend right before a race having the ideal hardness by simply melting and mixing different hydrocarbon ski waxes.
Since perfluorocarbons are not miscible with hydrocarbon waxes, this on-site adjustment opportunity to specific snow conditions is not possible.
While perfluorocarbon waxes used commercially are very hard and high melting and should therefore have a better abrasion resistance than softer hydrocarbon waxes recommended for wet snow, they have a disadvantage which limits their durability; perfluorocarbon waxes in contrast to hydrocarbon waxes are not compatible with polyethylene ski bases. Therefore, polyethylene ski bases cannot be saturated with perfluorocarbon waxes, which would provide the increased durability especially important in cross country racing.
While perfluorocarbon waxes are inert and non-toxic products, they can represent a serious health hazard, if not properly handled. Perfluorocarbons used commercially as ski waxes have a melting range of up to 108.degree. C. and have, therefore, to be heated by heating irons having a recommended minimum temperature of 150.degree. C. Because perfluorocarbons have no hydrogen bonding, they have a great tendency to sublime at elevated temperature. The inhalation of airborne perfluorocarbon particles and especially decomposition products formed during the application of perfluorocarbon waxes can represent a serious risk of pulmonary edema as documented by K. P. Lee and W. C. Seidel (Haskell Lab. Toxicol. Ind. Med., DuPont Co., Newark, Del. 19714 U.S.A.).
European Patent Application 0 421 303 A2 describes lubricants for skis, which comprise a fluorine compound containing a polyfluoroalkyl group and having a melting point of at most 100.degree. C., wherein the fluorine compound is at least one member selected from the group consisting of an alcohol containing a polyfluoroalkyl group, an ester containing a polyfluoroalkyl group, and a polyfluoroalkyl ester copolymer of (meth)acrylic acid. This application claims that perfluorocarbons as claimed in U.S. Pat. No. 4,724,093 having the formula C.sub.2n F.sub.2n+2 are having drawbacks as ski lubricants because of poor adhesion to the ski bases, possible degradation of the polyethylene ski base due to the high temperature required for their application, and, finally, poor abrasion resistance.
Fluoroalcohols and fluoroesters claimed in European Patent 0 421 303 have melting points of 50.degree. C. or less which makes them unsuitable for use as ski waxes per se, not having the desired melting point range of 50.degree. to 100.degree. C. In addition, the recommended fluoroalcohols are not miscible with hydrocarbon waxes.
The lubricants of this invention, be they hard solids, waxes or wax and resin additives are structurally different from prior art lubricants providing low friction properties for applications such as ski waxes or ski wax additives. Depending on the structure, they are miscible with hydrocarbon ski waxes.
In addition, the compounds of this invention offer other advantages over prior art ski waxes. The urethane, thiourethane and urea linkage groups provide very strong hydrogen bonding, which reduces sublimation and the potential health problems associated with perfluorocarbons when applied to skis by the hot melt process.
The lubricants of this invention, when used as ski waxes, can be applied using conventional wax application methods, such as the hot melt method, applying the wax with a hot iron to the ski base, or by spraying a solution of wax in a solvent onto the ski base, or by impregnating paper, nonwovens and other substrates with the ski wax and transferring the ski wax to the ski base with a hot iron.
Lubricants of this invention, in addition to being miscible with hydrocarbon waxes, can also be blended or milled with perfluorocarbon waxes and it is understood that conventional additives used in ski waxes to improve abrasion resistance, hardness, low friction properties, etc., can also be added to lubricants of this invention. Such additives can be powdered polyethylene, polytetrafluoroethylene, graphite, fluorinated graphite, and other inorganic or organic additives.